3.2 Environmental transmission of pathogens

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3.2 Environmental transmission of pathogens
Where do the pathogens come from? How do
pathogens in excreta contaminate the environment?
Learning objective To know and be familiar with
environmental transmission routes for pathogens,
especially in relation to water and sanitation.
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Origin of pathogens in wastewater- contribution
from different waste fractions

• Faeces
• contain the major amount of pathogens, enteric
  infections
• Urine
• only a few diseases transmitted through urine
• Greywater
• e.g. laundry, washing diapers, from food stuffs
• Industry
• abattoir, food industry (plant pathogens)
• Storm water
• e.g. surface run-off animal faeces

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Relative inputs of faecal indicator bacteria by
source
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The F-diagram - main routes to spread
diarrhoea
The main ways diarrhoea is spread by faecal
pathogens contaminating fingers, flies, fields,
food and fluids and then eventually swallowed
(Esrey et al. 1998)
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Transmission routes for pathogens in human excreta
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Contamination of groundwater
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Contamination of drinking water

• Drinking water quality
• Heterotrophic bacteria, E. coli, metals, nitrate
  (other aspects smell, colour)
• Contaminated surface- or groundwater
• Wastewater outlet, latrines, run-off
• Contamination during distribution
• Growth in pipes, intrusion of wastewater
• Contamination of finished water
• During storage and handling, e.g. reservoirs,
  vendors

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Waterborne diseases and sanitation
Waterborne diseases caused by the ingestion of
water contaminated by human or animal faeces or
urine containing pathogenic bacteria or viruses
include cholera, typhoid, amoebic and bacillary
dysentery and other diarrhoeal diseases.

• A sanitation system including reuse need to avoid
  disease transmission mainly by
• protecting ground- and surface water
• safe handling and use of the waste products in
  agriculture

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Possible transmission routes for pathogens from
organic fertilisers (e.g. faeces)
Handling on site

• The handling and reuse of all types of waste
  products with human or animal origin involve
  hygienic risks

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Contamination of food

• Contaminated seeds, uptake of pathogens?
• Organic fertilisers human excreta, wastewater,
  animal manure
• Irrigation wastewater, contaminated surface
  water
• Handling and storage
• Cooking
• Storing of cooked food, growth of pathogens

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Pathogens in faeces

• May contain bacteria, viruses, parasitic protozoa
  and helminths that cause infections
• Diarrhoeal disease of main concern
• Faeces should be considered a health hazard
• Need to be treated before use as a fertiliser
• Easier to handle and treat if diverted from other
  waste fractions

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Excretion of pathogens in faeces
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Pathogens in mixed wastewater

• Small volumes of faeces contaminates large
  volumes of clean water
• Collection from a large number of persons
  pathogens continously present
• Smaller systems higher concentration of a
  specific pathogen
• Treatment not optimized for killing pathogens
• 10 of wastewater is treated (developing
  countries)
• 20 million ha (?) irrigated with wastewater

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Health risks related to untreated wastewater

• Local environmental pollution
• Accidental exposure
• High risk of down-stream pollution
• Exposure from e.g. swimming and intended
  household use
• Pollution of drinking water sources
• Surface run-of and ground water infiltration
• Contamination of irrigated crops
• Exposure from consumption and during irrigation

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Typical concentrations of microorganisms in sludge
(EC, 2001)
per g wet weight

• In wastewater treatment pathogens are
  concentrated in the sludge

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Microorganisms in urine

• Urine is sterile in the bladder
• Freshly excreted urine contains lt10 000
  bacteria/ml
• Urinary tract infections - not transmitted
  through theenvironment
• Leptospira interrogans - low prevalence
• Salmonella typhi, Salmonella paratyphi -
  developingcountries, faecal-oral transmission
  more common
• Schistosoma haematobium - fresh water
  snailneeded for development low risk for
  transmission of infectious diseases through
  urine

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Pathogens in urine and importance of urine as a
transmission route
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Health risks related to urine diversion
Risk of disease transmission through urine The
main risks of disease transmission from handling
and using human urine are related to faecal
cross-contamination of urine and not from the
urine itself.
EcoSanRes (2004)
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Features of excreta - hygiene
Microorganisms in excreta

• Urine
• Sterile in body
• Naturally containing some bacteria after
  excretion
• Few diseases transmitted through urine
• Low risk to handle

• Faeces
• Naturally containing high amounts of bacteria
• Many diseases transmitted through faeces
  (faecal-oral)
• May contain pathogenic bacteria, viruses,
  protozoa or helminths
• Significant risk to handle

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Pathogens in greywater

• Lower concentrations of pathogens than in faeces
• Faecal origin of pathogens (bathroom and laundry)
• Shower and bath, Washing clothes, washing diapers
• Pathogens from food stuffs (kitchen sink)
• Faceally contaminated vegetables (e.g. from
  irrigation with wastewater or animal manure),
  soil
• Contaminated meat (e.g. chicken)
• Health risk from disposal or reuse
• Contamination of nearby surroundings
• Contamination of drinking and recreational water
• Irrigation of crops

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Transmission by animals

• Zoonoses
• Transmission humans animals
• May cause symptoms or not in animal
• Vectors
• Insects, rodents, birds mechanical transport
• Birds, wild and domestic animals infected without
  symptoms
• Intermediate host
• Animal necessary for lifecycle of pathogen, e.g.
  malaria, schistosomiasis

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Outbreak of EHEC in Sweden
Irrigation of lettuce (no requiremenmts for
analysis of the water)
Run-off from agricultural land where grazing
cattle were infected with EHEC (a zoonoses, i.e.
transmissionn animal-human) Transport from manure
to river water
The lettuce was consumed by a large number of
individuals resulted in 100 cases (approx. 10
hospitilised)
At the lab isolating and comparing bacteria in
samples from patients and in water samples